Process for the separation and recovery of metals from metallic alloys



Patented July 21, 1942 PROCESS FOR THE SEPARATION AND BE:- COVERYOF METALS FROM METALLIC AL- LQYS John D. Gat, Edgewood, Pa.

No Drawing. Application December 3,1940, Serial No. 368,389

2 Claims.

This invention relates to the separation and recovery, in pure metallic state, of one of the elementary constituents of certain binary metallic alloys. The development relates particularly to the treatment of waste products of tin plate industry and to recovery of tin from such by-products of tin smelting practice as hardhead. a

During the manufacture of tin plate, the pots must be frequently cleaned from heavy metal, iron-tin compounds which have settled to the bottom, and from a suspension of tin oxide and metallic tin in palm oil floating on the top and known as scrufi. This operation, technically termed drossing, removes heavy metal together withcomparatively large amounts of tin held by capillary attraction among the crystals of 'the iron-tin compound. The tin so removed is recovered by heating this heavy metal in sweating furnaces so as to cause liquation. This treatment oxidizes the solid body of iron-tin compounds to some extent.

As the scruif so removed carries large amounts of palm oil, the inorganic constituents of it must be separated from the palm oil by burning the latter off in the same furnaces as used for liquating heavy metal. The residues remaining in the sweating furnaces after liquation and after burnbath, after which the liquid tin is tapped from beneath the crust.

These methods cannot be applied, however, to iron-rich tin alloys. In the processes of the prior art, alloys belonging to this category were either returned, as a part of charge, to the tin-melting furnac es,when hardhead had to be disposed of, or melted in the presence of lead, which dissolves tin in all proportions without dissolving any iron, a practice common to the tin plate industry. The first method involves an elaborate plant and removes only a portion of iron by transforming it into silicates. Reduction in the presence of lead results in a tin-lead alloy containing about percent tin; so that the utilization of the metal so produced is limited to terne coating and similar applications only. The process of my invention permits therecovery of tin in a pure state, even from high iron alloys.

ing off, both of which are somewhatoxidized, are

- roundabout manner.

When the iron concentration of the alloys is comparatively low, the element is separated from tin either by liouation or by segregation. In the methods involving liouation, the alloy. cast in bl cks. is heated slightly above the melting point of pure tin but considerably below the temperature at which.the iron-tin intermetallic compounds begin to melt. Molten tin flows from the solid framework of the latter and is separated from it. .In the segregation methods, the alloys of iron and tin are melted in reverberatory furnaces and then slowly. cooled, until a crust of iron-tin compounds is formed on the top of the The fundamental principles of my invention were discovered during the course of my efforts to develop an improved process for separating tin from iron contained in the tin-iron alloys. I have foundthat the problem can be efiectively and economically solved by introducing, under proper conditions, aluminum in the iron-tin system. Aluminum alloys both with iron and tin in any proportions, provided the temperature is sufliciently high, and forms, on cooling, intermetallic compounds with the iron which'are more stable than the intermetallic compounds of the latter with tin, so that iron-tin compounds cannot form added to the liquid bath to convert all iron present -into FezAle, allowing for' a slight excess re-' These characteristics permit both a complete" elimination .of the iron and of .the aluminumwhich has been introduced for the removal of v the former from the tin.

, According to .m,v invention, iron is separated from tin in the followingmanner; vThe irontin alloy to be treated is completely. liquefied by heating 'it to a sufliciently high temperatiiraeither with or without protection exerted by a suitably chosen covercf slagor any'othe'r appropriate substance. IA suflicient amount of aluminum is qulred for keeping the iron-tin compounds from forming. After aluminum is thoroughly incorporated, the bath is cooled below the solubility point of FezAla, but-above the melting point of tin, and is held at this temperature long enough to permit upward settling of the desired amount of the iron-bearing compounds. Instead of keep- 'ing the melt at a given temperature, it may be allowed to cool continuousl at a sufficiently slow rate. The crust of the iron-aluminum alloy formed in this way is sepaarted from the body of the underlying tin. This separation can be made before a complete separation is effected. In this case, the impure tin removed from under the crust is held just above its melting point long enough to permit all iron-bearing compounds and any possible excess of aluminum to rise to the surface, from which they are mechanically removed. The length of time required for this separation treatment depends on the degree of the desired purity of tin.

In order to adjust the process to optimum efficiency under the conditions existing in tin plate industry, I prefer to charge both heavy metal and scruff directly in a shaft furnace, a cupola, for example, together with some proper reducing material, such as coke, reduce tin oxides by keeping a strongly reducing atmosphere, melt tin and tin-iron alloys, keeping temperature sufficiently high to volatilize all zinc, tap the metal in an appropriate container, add to it a sufficiency of aluminum to combine with all iron and to leave a slight excess, cool the liquid alloy until a heavy crust of solid iron-aluminum alloy is formed on its surface, separate from it the body of still liquid tin underlying it by proper means and free this tin from the last traces of iron and aluminum by holding the metal at a temperature slightly above its melting point and mechanically removing from its surface solid phases rising to it, the use of some protecting cover, such as palm oil, being optional during the last operation.

'It is well known that, for many metallurgical processes, the use of aluminum-iron alloys is preferable to the introduction of commercially pure aluminum. However, the general adoption of this practice in steel plants heretofore has been handicapped by the costs involved in the preparation of such alloys. I have discovered that the ferro-aluminum alloy produced by the processes of the present invention eliminates this handicap and offers an' improved deoxidizing agent for the deoxidizatlon of steel. V

Iclaim:

l. A process for separating tin from an irontin. alloy, including heating the alloy to render it liquid, adding aluminum to the liquid to produce an iron-aluminum compound dissolved in tin, cooling the liquid to a temperature below the solubility point of the compound in the tin, but substantially above the melting point of the tin, holding the liquid at this temperature until a portion of the compound separates from the liquid tin, removing this portion from the liquid tin, further cooling the liquid to a temperature just slightly above the melting point of tin, so that the remainder of the compound separates from the tin, and removing this remainder from the tin.

2. A process for separating tin from an iron-tin alloy, including heating the alloy to render it liquid, adding aluminum to the liquid to produce an iron-aluminum compound. dissolved in tin, cooling the liquid to a temperature below the solubility point of the compound in the tin, but 

